The vacuum infusion process has been widely used in the molding process of fiber-reinforced resin composite products. Generally speaking, the process is: first, disposing a certain number of layers of fibers on the mold in accordance with the design requirements to form a fiber preform, wherein the fiber preform may contain core materials such as foam, balsa or other reinforcing materials; in addition, there are also process materials such as a peel ply or release film, flow mesh, resin runner, injection port, resin tube, vacuum tube, suction port etc. disposed on the fiber preform; then, sealing the aforesaid fiber preform and process materials by using a vacuum bag and a sealant tape to form a completely sealing system; connecting the suction port with a vacuum pump to draw out the air within the aforesaid sealing system, and thus to reach a vacuum pressure of −0.05 MPa to −0.1 MPa; then, inserting the resin tube into an opened vessel filled with resin; the resin is vacuum sucked into the aforesaid sealing system via the resin tube under the action of atmospheric pressure, and impregnates the fiber preform quickly in the aid of the resin runner resin runner and the flow mesh; then, according to the characteristics of the resin that is used, curing the resin at room temperature or by heating the mold; removing the aforesaid process materials and taking the cured product out from the mold to obtain the final product.
The key of the above process is: to reasonably establish the resin flow-guiding system, namely the positions and sizes of the process materials such as the injection port, the resin runner, the flow mesh, the vacuum tube, the suction port etc., so that the air within the aforesaid fiber preform can be discharged smoothly during the infusion process, and that the resin can completely impregnate the entire fiber preform before it gels, thus avoiding the occurrence of dry fiberglass, white spots and other defects.
With the expansion of the application arts of composite materials, the application of composite materials in yachts, fishing boats, aviation and wind power and other fields becomes wider and wider, and the sizes of the products are also growing. The increase of the product size, particularly the increase of the thickness, will make it much more difficult to discharge the air from the sealing system, and extend the flow time of the resin inside the fiber preform. Restrained by the viscosity and gel time of the resin, vacuum infusion of products with greater thicknesses becomes more difficult.
In the prior art, there are some solutions provided for trying to solve the aforesaid technical problem.
For example, Chinese patent application CN101708658A discloses a method for manufacturing a spar cap of a wind turbine blade, wherein a flow mesh is disposed below a fiber preform to assist the flow of the resin, and a semi-permeable membrane, which is permeable to air but is non-permeable to the resin, is disposed above the fiber preform for air-pumping. By using said manufacturing method, the resin impregnates the fiber preform from the bottom of the fiber preform to the top. The semi-permeable membrane disposed above the fiber preform can continuously discharge the air within the fiber preform to avoid that a part of the air was surrounded by resin due to the uneven flow of the resin, and thus results in white spots or dry glass fibers and other defects. This manufacturing method is generally adopted in the present technical field.
However, this method also has the following restrictions: since the resin needs to impregnate the entire fiber preform from bottom to top, the resin needs to flow through the entire thickness of the fiber preform. Limited by resin viscosity and gel time, when the resin cannot completely impregnate the entire thickness of the fiber preform within its gel time, the application of this method will be restricted.
In another example, Chinese patent application CN103817955A discloses an infusion method for a carbon fiber spar cap of a wind turbine blade, wherein flow meshes are disposed both below and above a fiber preform to assist the flow of a resin. Compared to a glass fiber, the filament diameter of a carbon fiber is smaller, and the distance between the filaments is also smaller. Thus, it will be much more difficult to make the resin flow between the carbon fibers and impregnate the resin. Therefore, the carbon fiber preform is generally harder to be infused than the glass fiber preform.
A significant drawback of this method is: from the beginning of the infusion, the resin flows to the middle of the fiber preform from both the top and the bottom simultaneously. During the entire process of infusion, the air in the most middle part of the fiber preform can hardly be discharged effectively. Such results are: the middle part of the fiber preform is not sufficiently impregnated, and thus forms white spots or dry glass fibers.
International PCT patent application WO2004/033176 discloses another infusion method for a carbon fiber preform, wherein flow meshes are disposed both below and above a fiber preform to assist the flow of a resin. By using said method, first, the resin is injected from the flow mesh below the fiber preform; thus, the resin will impregnate the fibers from the bottom of the fiber preform to top, making the air within the fiber preform discharged via the above flow mesh and suction port. Until the resin impregnates about two-thirds of the thickness of the fiber preform, the resins is injected from the flow mesh above the fiber preform, and thus enable the resin to impregnate the remaining fibers from the top of the fiber preform to bottom.
This method avoids the problem that the fibers in the middle of the fiber preform cannot be sufficiently impregnated caused by the injection of the resin from both the top and the bottom of the fiber preform simultaneously, but also brings some new technical problems: first, the injection port and the suction port arranged above the fiber preform will tightly press against the fiber preform under the action of atmospheric pressure to form imprints, making the fibers bend and affecting the mechanical properties and the surface quality of the products; second, in said method, both of the injection port and the suction port above the fiber preform are connected with the flow mesh above the fiber preform to strengthen the speeding of discharging the air within the fiber preform at the beginning stage of resin injection. Practices prove that by using said method, the resin injected though the injection port above the fiber preform will flow into the suction port through the flow mesh very quickly, resulting in the interruption of the vacuum pumping. At the moment, the air within the fiber preform can no longer be discharged, producing dry glass fibers or white spots or other defects below the flow mesh.
In another example, Chinese patent application CN104325658A discloses a method for manufacturing a spar cap of a wind turbine blade, wherein flow meshes are placed both below and above a fiber preform to assist the flow of a resin. By using said method, first, the resin is injected from the flow mesh below the fiber preform; the resin impregnates the fibers from the bottom of the fiber preform to top. When the part of the fiber preform near the injection port is completely impregnated with the resin and the resin flows to the flow mesh above the fiber preform, start injecting the resin from the above flow mesh. Thus, the resin impregnates the fibers from the top of the fiber preform to bottom and finally realize the complete infusion.
A significant drawback of this method is: the injection tube placed above the fiber preform needs to suspend above the fiber preform to avoid the formation of imprints caused by the direct contact of injection tube and injection port with the fiber preform, and ultimately affecting the mechanical properties and surface quality of the products. Practices prove that it is very difficult to carry out said method during the manufacturing process, and thus it can hardly be used in practical production. In addition, said method uses the way of placing a single layer of discharge passage on the side of the top of the fiber preform which is far away from the injection port. Because of the irregularity of the flow of the resin, said discharge passage can easily be blocked by the resin penetrating from the bottom of the fiber preform, causing the air near said passage impossible to be discharged continuously. Meanwhile, since the position of said discharge passage is farthest away from the injection port of the resin, i.e., the last part to be impregnated in the entire fiber preform, the result of the discharge passage being blocked by the resin is that the glass fibers near the position of said discharge passage can easily form dry glass fibers or white spots because the air cannot be sufficiently discharged.
Based on the aforesaid prior art, when infusing a fiber (e.g., carbon fiber) preform which has a relatively large thickness or can hardly be impregnate by the resin, it is urgently required to develop a method for manufacturing fiber-reinforced plastic/resin products which not only can realize the complete and sufficient impregnation of the fiber preform and avoid the production of the defects like dry glass fibers and/or white spots, but also is conducive to the implementation during the manufacturing process.